Traffic control system



P 1965 J. B. RUDDEN ETAL 3,206,721

TRAFFIC CONTROL SYSTEM Filed May 28, 1962 2 Sheets-Sheet 1 22 CENTRAL =MTELEPHONE. COMMUNICATION 22 EXCHANGE COUPLER TERMINAL 2o a1; DATA PRocEssme EQUIPMENT 0 4 STREET B L F/e.a) f.

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B GREEN 1 F LTER 7 A GREEN COMMUNlCATION LINK JAMES B. RuDDE/V 0A N/EL L. GE/QL 0616 1 47 INVENTORE A RED BAMBER AGENT United States Patent 3,2il6,721 TRAFFEC CUNTROL SYSTEM James B. Rndden, (lair Park, BL, and Daniel L. Gel-laugh,

Pacific Palisades, Caiizh, assignors, by mesne assignmeets, to The Bunkeritanic Corporation, Stamford,

Conn a corporation of Delaware Filed May 28, 1962, Ser. No. 197,959 4 t'llaims. (Cl. 34035) This invention relates generally to a trafiic control system and more particularly to a system employing data processing equipment for controlling intersection trafiic lights.

It is well recognized that the intersection represents the key to efficient vehicular movement. That is, regardless of the extent of improvements to the general flow of traftie, the street system cannot be utilized to its maximum efficiency unless the intersections are properly controlled. The effectiveness of controlling trafiic movements at intersections determines the street system capacity, establishes the level of service to the motorists, influences vehicular operating costs, and affects the safety of vehicular travel.

In conventional trafiic systems, intersection traffic lights are controlled by local controllers which determine the duration of the various intervals. Most controllers are generally provided with means for varying the total traffic light cycle length, the cycle split (i.e., the time relationship between the main street green interval, the side street green interval, the amber intervals, and any other intervals employed) and the offset (i.e., the time relationship between a given traffic light cycle and a reference traffic light cycle) and in use are preadjusted to permit the greatest flow per unit time for normal conditions, consistent with safety.

Although preadjusted local control systems of this type perform satisfactorily under normal trafiic conditions, they are ineffective to properly cope with abnormal traffic conditions which can be caused by am. and p.m. rush hours, inclement weather, accidents, and major events, e.g., ball games, parades, concerts, etc.

Accordingly, in modernizing traffic light control systems, the desirability of providing a system which is at all times responsive to traffic conditions has been recognized. Additionally, it is desirable that such a system be capable of exercising control over a plurality of intersections from a remote central location.

One such modernized system which has been proposed makes use of data processing equipment responsive to various traffic detectors to exercise central control over all traffic light intervals at a plurality of intersections via some communication link. This system appears to be only partially satisfactory because of the high cost of the relatively extensive data processing equipment required to control every interval and because of the heavy requirements made on the communication link as a result of the high rate of information transfer required. In addition, since all intervals are controlled by the data processing equipment, a failure in this equipment or the communication link could cause a failure in the entire trafiic system.

In the light of the deficiencies of presently known traflic light control systems, it is an object of this invention to provide an improved system in which control over a multitude of intersections is exercised from a central location in accordance with traffic conditions.

It is an additional object of ths invention to provide data processing means adapted to be incorporated in conventional traflic light control systems, characterized by local control, in order to centrally control a plurality of intersection tratlic lights in accordance with traific conditions.

It is still an additional object of this invention to pro ice vide a trailic light control system employing data proc: essing equipment in a more eiiicient manner than in heretofore discussed systems to thereby considerably reduce the system cost and improve system reliability such that the system does not entirely fail in the event of failure of the data processing equipment or communication link.

Briefly, the invention herein is based on the premise that an optimum traffic flow can be established by controlling intersection trafiic lights in accordance with characteristics of the trafiic such as volume or density and comprises a traflic light control system in which local intersection controllers exercise primary control over all trafiic light intervals and data processing equipment, responsive to traffic characteristics, exercises overriding control so as to modify the duration of certain intervals.

More particularly, the invention herein makes use of the type of intersection controller commonly utilized in most present traffic control systems wherein a controller is generally located at each intersection. A controller comprises a cyclic timing device which operates to energize the appropriate illuminating means for predetermined intervals. For example, at a simple intersection of street A with street B, the controller can go through a 60- second cycle comprising a 30-second street A green interval, a S-second street A amber interval, a 20-second street B green interval and a S-second street lB amber interval. As noted, controllers are usually provided with manual means for varying the duration of the various intervals and these means are preadjusted for normal traffic conditions. It has been determined that in order to most effectively move traffic, the duration of certain intervals must be modified in accordance with trahic conditions while others need not be. More particularly, the amber intervals can remain of constant duration regardless of trafiic conditions. The invention herein teaches that a plurality of controllers can be most eifectively controlled by inhibiting the cycling to cause each controller to always hold itself in a green interval until a release command addressed to it is generated by the data processing equipment.

In a preferred embodiment of the invention, the data processing equipment provided develops and stores information based on traffic conditions regarding the time of day the next control command associated with each controlled intersection is to be executed. A comparison means compares each stored execution time with the out put of a time of day clock and causes signals representative of the control commands to be generated at the appropriate time. Each signal in turn permits the controller to which it is directed to release its green interval. Subsequent to the performance of each command, the stored execution times are updated by the data processing equipment based upon traific conditions as detected by a plurality of traffic characteristic detectors distributed throughout the street system of the controlled area. The updating procedure makes use of computational capabilities of the data processing equipment to compute, according to a stored program, subsequent execution times to most effectively move tratlic under the existent conditions.

Other objects and advantages, which will subsequently become apparent, reside in the details of circuitry and operation as more fully hereinafter described and claimed, further reference being made to the accompanying drawings forming a part hereof, wherein like identfiying numerals refer to like parts throughout the several figures, and in which:

FIGURE 1 is a schematic illustration of a traffic light control system embodying the inventive concepts herein;

FIG. 2 is a schematic illustration of a local controller and shows the manner in which data processing equipment can be coupled thereto for modifying the normal operation thereof;

FIG. 3 is a schematic illustration of a preferred embodiment of data processing equipment which can be em ployed in the system of FIG. 1; and

FIG. 4 comprises a table representing exemplary information stored on the magnetic drum of the data processing equipment of FIG. 3.

With continuing reference to the drawings, initial attention is called to FIG. 1 wherein a traffic light control system embodying the concepts of the invention is illustrated for controlling traffic along street A. As previous ly pointed out, in order to most efficiently control the trafiic on street A, it is essential to properly regulate the intersections, i.e., with streets B, C and D. In order to do this, conventional traific lights are situated at each intersection. The selective illumination of the signals representing the various traific intervals is controlled by a local controller 12 which can be connected to the intersection lights 10 by a direct cable 14 or other suitable means.

In most conventional systems, the local controllers each operate according to preadjusted conditions. The invention herein provides for data processing equipment 16 to exercise supervisory or overriding control over the local controllers 12. This control is in the nature of a modification of the total cycle duration, the cycle split or the offset of the local controller. Total cycle duration is defined as the elapsed time required for the local controller to complete one cycle; e.g., the elapsed time between successive beginnings of the street A green interval. Cycle split is defined as the time relationship between the main street green interval, the side street given interval, the amber intervals, and any other intervals employed; e.g., with respect to the equipment associated with the intersection between streets A and B, the cycle split refers to the duration of the street A green interval, street A amber interval, street B green interval and street B amber interval. Offset is defined as the time relationship between a given trafiic light cycle and a reference traffic light cycle; i.e., assuming the equipment at the intersection of streets A and B is considered the reference, the offset refers to the elapsed interval between the time the equipment at intersection AB starts a street A green interval and the time that the equipment at intersection AC starts a street A green interval.

The data processing equipment 16 communicates with the local controllers 12 via any appropriate communication link such as the telephone circuit illustrated, a direct cable connection, microwave or other radio communication, or various other means. The particular communication link utilized in any situation would probably best be determined by economic considerations. Regardless of which type of communication is employed, it should be apparent that some type of suitable coding should be utilized so that the data processing equipment can direct commands to selected local controllers.

A telephone communication link is illustrated and includes a central communication terminal 18 by which the data processing equipment is able to put information on the telephone lines. From the central communication terminal 18, the control commands to the local controllers are treated as any other conventional phone call; that is, they are directed to a telephone exchange 20 via telephone lines 22 and thence to the local controllers 12, each of which may be considered as a telephone subscriber.

The control commands generated by the data processing equipment, which is to be more particularly described in conjunction with FIG. 3, are determined on the basis of traffic conditions. In order for the data processing equipment 16 to be cognizant of the trafiic characteristics, one or more detectors 24, which can, for example, be of conventional treadle, radar, or magnetometer design are coupled to the data processing equipment 16 via telephone lines 22 or other appropriate communication means.

Attention is now drawn to FIG. 2 wherein a local controller 12 is schematically illustrated. The local controller 12 functions to define the various signal intervals required at an intersection. More particularly, at a simple intersection, for example, the intersection between streets A and B illustrated in FIG. 1, it may merely be necessary to define street A green and amber intervals and street B green and amber intervals. It should be realized that the street B red interval is identical to summation of the street A green and amber intervals and similarly the street A red interval is identical to the summation of the street B green and amber intervals. At more complex intersections, several more intervals might be provided; e.g., pedestrian walk intervals, green turn intervals, etc. For purposes of simplicity, the local controller 12 illustrated is designed to define only four intervals, it being appreciated that its design could be easily extended to define as many intervals as required.

The local controller 12 comprises a conductive arm 32 rotatable about pin 34. A battery or other source of potential 36 is electrically connected to the arm 32. Means (not shown) are provided for rotating the arm 32 about pin 34 (in the direction of the arrow) at a uniform speed. Conductive arcuate sections 38, 40, and 44 are disposed about the pin 34 and in a position so as to be engaged by the cnductive arm 32 as it moves in its rotational path about pin 34.

The street A green traffic light is connected to arcuate section 38 such that whenever arm 32 is engaged with section 38, it will be illuminated. Similarly, the street A amber tratfic light is connected to section 40, the street B green trafiic light to section 42, and the street B amber traffic light to section 44. As previously pointed out, it is necessary to illuminate the street B red traflic light when either the street A green or amber traific lights are illuminated. Accordingly, the street B red traific light is connected to arcuate section 33 through diode 46 and section 40 through diode 48. Similarly, the street A red traffic light is connected to section 42 through diode 47 and to section 44 through diode 49.

In operation, it will be appreciated that as arm 32 moves in its rotational path, it will successively cause the various tralfic lights to be illuminated. From the previous definition given for total cycle, it will be realized that the total cycle duration is the time required for the arm 32 to sweep through 360. It will be realized that one simple way to vary the total cycle duration is to merely vary the rotational speed of arm 32. It will be noted that the various sections are not of the same arcuate length and it should be apparent that this is because the arcuate length of a section defines the illumination interval of the traffic light connected to it. From the previous definition given for cycle split, it will be apparent that a cycle split can be modified by changing the relative arcuate lengths of the sections.

An implementation for varying the total cycle duration and cycle split which is particularly adaptable to control by data processing equipment includes a solenoid 50 having an armature 52 capable of being projected into the path of movement of the arm 32. By providing a slip clutch means (not shown) between the arm 32 and its driving source (not shown), cycling can be inhibited so that the total cycle duration can be extended and a particular interval can be selectively extended so as to modify the cycle split. Inasmuch as it has been found that regardless of traffic conditions, it is generally not necessary to modify the amber or vehicle clearance intervals, and that appropriate trafiic control can be effected by merely controlling the green intervals, solenoids 50 are positioned adjacent the termination points of both arcuate sections 33 and 42 respectively defining the street A and street B green intervals. By providing a spring 54 between armature 52 and surface 56, the armature 52 is normally biased out of the rotational path of arm 32. The solenoid coil 58 wound about the armature 52, when properly energized, causes the armature to be projected into the rotational path of arm 32 to hold the controller 1 2 in check in a green interval. In order to be able to selectively energize the coils 58 from a remote location via some communcation link, e.g., telephone lines, filter means 59, capable of selectively passing a signal of a unique frequency is connected to each of the coils. Interruption of the signal applied to coil 58 permits the controller 12 to resume its normal operation. Accordingly, by causing the data processing equipment 16 to selectively control tone generators 60 (FIG. 3) connected via some communication link to the solenoid coils 58, the cycle lengths, cycle splits and offsets of each controller can be selectively controlled.

From the foregoing, it should be appreciated that the duration of certain intervals (e.g., amber intervals) are determined entirely by the local controller while the duration of other intervals (green intervals) are controlled by the local controller in conjunction with the data processing equipment. The utilization of this configuration rather than a configuration in which the data processing equipment defines the duration of all intervals, permits data processing equipment of more modest dimensions to control the same number of intersections, simplifies the requirements of the communication link and in addition permits the local controllers to operate according to their predetermined cycle conditions in the case of a failure in the communication link.

Attention is now called to FIG. 3 wherein a preferred embodiment of data processing equipment suitable for use in the system of FIG. 1 is schematically illustrated. It should now be realized that the broad function of the data processing equipment 16 is to respond to information from the detectors 24 to properly energize the solenoid coils 58 in each controlled local controller 12. It has been pointed out it is desirable that the local controllers 12 operate in accordance with their normal cycles in the event of a communication link failure and accordingly the armatures 52. of solenoids 50 are normally biased out of the path of conductive arm 32 by springs 54. Associated with each coil 58 of each controller 12 is a tone generator 60, located proximate to the data processing equipment, capable of generating a continuous tone of a unique frequency, e.g., f f f etc. Filter means 59 connected to each of the coils 58 of each controller is uniquely responsive to the frequency of the generated tone of the associated generator. When the communication link is effective, the continuous tone applied to the terminals of each solenoid coil 58 through filter means 59 via the communication link causes the arm 32 to be detained in each green interval until the tone is interrupted. The data processing equipment shown in FIG. 3 functions to selectively interrupt the tone generators 60 at particular times as determined by the trafiic conditions.

The data processing equipment comprises an information storage means in the form of a continually rotating;

magnetic storage drum 62, an arithmetic and control unit 64, a time of day clock 66, a comparator device 68, gating means 70 and decoding means 72. Inasmuch a all of these components are conventional devices available in most all general purpose magnetic drum digital computers, and thoroughly described in most digital computer texts (e.g., see Digital Computer and Control Engineering by Robert S. Ledley, McGraw-Hill, 1960), no discussion of their structural details will be offered herein. It will suflice to set forth the interconnections between the components and describe their functions and relationships to one another.

The general objective of any traffic signal control system is to maximize the number of vehicles passing through the intersection per unit time, and to improve the level of service to the motorist. In the absence of any better measure of service, minimum total delay at the intersection is taken as a measure of optimum service.

The literature contains several methods of determining the cycle length and split of individual traffic signals by algebraic methods. (H. K. Evans, Editor. Traffic Engineering Handbook, Institute of Traffic Engineers (1950), pp. 223-229. T. M. Matson, W. S. Smith, and F. W. Hur-d. Traflic Engineering, McGraw-I-lill Book Company, New York (1955), pp. 327-354). Some of these methods are based on the assumption of uniform arrival of traflic, given a total volume. Other methods are based on statistical considerations, assuming random arrivals, and it is suggested that the signal be timed such that of the cycles will pass all traffic arriving during that cycle (T. M. Matson, W. S. Smith, and F. W. Hurd. Traffic Engineering, McGraw-Hill Book Company, New York, 1955, pp. 327354). Still other methods, e.g., a method derived by Webster (F. V. Webster. Traffic Signal Settings, Road Research Technical Paper No. 39., H. M. Stationery Ofiice, London England, 1958) makes use of a developed formula for delay at an intersection which contains a term based on theoretical considerations of average (uniform spacing) only, a term based on queueing theory and considerations of random properties of trafiic, and a correction term based on empirical observations.

Regardless of which method of analysis is used, a program can be developed for the computation by arithmetic and control unit 64 of cycle lengths, splits, and offsets. The sequence of instructions comprising such a program is stored in track 2 of drum 62 and read by read head 74. Read head 76, positioned to read the data from track 1 written by detectors 24 via Write head '78, is also connected to unit 64 and based on this data, unit 64 performs the prescribed computations and stores the computed data in track 3 via write head 80, associating the computed data for each intersection with the appropriate intersection command stored in track 5 and read by read head 84. For a clearer picture of the data stored on drum 62, attention is called to FIG. 4 comprising a table illustrating an exemplary organization of information stored thereon.

It will be noted that drum track 5 stores a plurality of coded control commands, including two commands per intersection. Each command corresponds to a tone generator 60 each of which it will be recalled is uniquely associated with a solenoid coil 58. It will further be noted that drum track 3 stores the offsets and cycle durations for each intersection green interval. Additionally, drum track 4 stores the time at which the next command at each intersection is to be executed.

In operation, as the drum 62 continually rotates, read head 82, connected to comparator 68, reads the execution times stored in track 4. Comparator 68 continually compares the output of read head 32 with the output of time of day clock 66 and when they are identical, the comparator output terminal 69 is energizezd. Simultaneously, read head 84 reads the commands from track 5. Both read head 84 and comparator output terminal 69 are connected to the input terminals of gating means 70. Accordingly, energization of output terminal 69 enables gating mean-s '70 to pass command signals at the appropriate time to decoding means 72. The decoding means 72 decodes the command signal and in turn energizes its output line uniquely designated by the signal. Each decoding means output line is uniquely connected to a relay coil 86 positioned to control a normally closed switch 88 connecting the tone generator 6t) to a power supply 13+. Energization of a decoding means output. line therefore opens a switch 88 so as to interrupt the tone generated by the tone generator 60 connected thereto. It will be recalled that interuption of a tone permits the withdrawal of the associated armature 52 (FIG. 2) to thereby release the green interval of the associated controller.

Subsequent to each positive identity between the output of the time of day clock 66 and an execution time, as recognized by comparator 68, the execution time data must be updated. The arithmetic and control unit 66 performs this function under stored program control, i.e.,

according to the instruction sequence stored in track 2 together with offset and cycle split information stored in track 3 and read by read head 81.

As an example, note that according to the exemplary data provided in FIG. 4 (wherein the binary coded decimal data represents the information actually stored on the drum and the other data is provided merely to facilitate an understanding of the equipment) when the output of the time of day clock 66 indicates that it is 3 :25:36, the coded command 001 will be applied to the decoding means 72 thereby causing the interruption of the tone from the tone generator 60 to which the coil 58 associated with the street A green interval at intersection AB is responsive. Energization of comparator output terminal 69 will additionally cause unit 64 to refer to the information in track 3 to compute the time at which the street A green interval should next be released, taking into account the duration of constant intervals such as amber intervals which herein have always been assumed to be 5 seconds. In updating the execution times with respect to intersection A-C and A-D, assuming intersection AB to be the reference, the offset must additionally be considered.

Although the data processing embodiments illustrated herein are of the digital drum type, it should be readily apparent to one skilled in the art that other digital and analog devices capable of performing the necessary func tions could be utilized in their stead. Regardless of which particular data processing equipment is utilized, the control of a traflic light system by data processing equipment by exercising supervisory or overriding control over local controllers permits tratlic to be moved much more efficiently than in previously known systems at a relatively modest expense.

The foregoing is considered as illustrative only of the principles of the invention. Since numerous modifications will readily occur to persons skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described and accordingly all suitable modifications and equivalents are intended to fall Within the scope of the invention as claimed.

The following is claimed as new:

1. A trafiic control system comprising:

at least one intersection traffic light;

a free running cyclic timing means defining a plurality of discrete time intervals connected to said trafiic light;

a trafiic detector means for providing an output signal indicative of a traffic characteristic;

data processing means responsive to the output of said detector means for modifying the duration of certain ones of said intervals; said data processing means including first means operable to extend the duration of said certain intervals by interrupting the free running of said timing means; second means actuatable to interrupt the operation of said first means; information storage means storing information representing times for actuating said second means; a

time of day clock; comparator means for comparing the output of said clock with said times stored by said storage means; means responsive to said comparator means for actuating said second means; and stored program computing means responsive to said detector means output signal for modifying said information stored by said information storage means.

2. A traffic light control system comprising: a plurality of traffic lights, each located at a different intersection; a plurality of free running cyclic timing means, each respectively connected to a different one of said tratfic lights, each of :said timing means defining a plurality of discrete time intervals and having actuatable means for extending the duration of certain ones of said intervals; at least one traflic characteristic detector; data processing means responsive to the output of said detector for controlling the duration of said certain ones of said intervals defined by each of said timing means; said data processing means including an output means coupled to said extension means for actuating said extension means; said data processing means further including stored program computing means for computing the duration of said certain intervals and the relationship between the cycles defined by each of said timing means based on the output of said detector; information storage means storing signals associated with said output means representative of execution times at which said output means should be actuated; a time of day clock; comparator means for comparing the output of said clock with said signals representative of each of said execution times and for developing an output signal upon occurrence of said identity therebetween; and means responsive to each of said comparator means output signals for updating said signals representative of said execution times based on the duration of said certain intervals and for actuating said output means.

3. The system of claim 2 including means for generating a coded signal in association with the development of each of said comparator means output signals; and

responsive means associated with each of said timing means and each uniquely responsive to one of said coded signals.

4. The control system of claim 3 wherein said means for generating coded signals includes a plurality of tone generators each capable of generating a signal of a unique frequency; and

said responsive means comprises filters responsive only to signals of a certain frequency.

References Cited by the Examiner UNITED STATES PATENTS 2,506,368 5/50 Leonard 340--37 3,079,587 2/63 Barker 340- 3,090,032 5/ 63 Shand 340-35 NEIL C. READ, Primary Examiner.

THOMAS B. HABECKER, Examiner. 

1. A TRAFFIC CONTROL SYSTEM COMPRISING: AT LEAST ONE INTERSECTION TRAFFIC LIGHT; A FREE RUNNING CYCLIC TIMING MEANS DEFINING A PLURALITY OF DISCRETE TIME INTERVALS CONNECTED TO SAID TRAFFIC LIGHT; A TRAFIC DETECTOR MEANS FOR PROVIDING AN OUTPUT SIGNAL INDICATIVE OF A TRAFFIC CHARACTERISTIC; DATA PROCESSING MEANS RESPONSIVE TO THE OUTPUT OF SAID DECTECTOR MEANS FOR MODIFYING THE DURATION OF CERTAIN ONES OF SAID INTERFAALS; SAID DATA PROCESSING MEANS INCLUDING FIRST MEANS OPERABLE TO EXTEND THE DURATION OF SAID CERTAIN INTERVALS BY INTERRUPTING THE FREE RUNNING OF SAID TIMING MEANS; SECOND MEANS ACTUTHE FREE ATABLE TO INTERRUPT THE OPERATION OF SAID FIRST MEANS; INFORMATION STORAGE MEANS STORING INFORMATION REPRESENTING TIMES FOR ACTUATING SAID SECOND MEANS; A TIME OF DAY CLOCK; COMPARATOR MEANS FOR COMPARING THE OUTPUT OF SAID CLOCK WITH SAID TIMES STORED BY SAID STORAGE MEANS; MEANS RESPONSIVE TO SAID COMPARATOR MEANS FOR ACTUATING SAID SECOND MEANS; AND STORED PROGRAM COMPUTING MEANS RESPONSIVE TO SAID DECTOR MEANS OUTPUT SIGNAL FOR MODIFYING SAID INFORMATION STORED BY SAID INFORMATION STORAGE MEANS. 